1. Field of the Invention
The present invention relates generally to reproduction of information stored on a magnetic recording medium, and more particularly to magnetic storage apparatus in which information is reproduced by a magnetoresistive element in a magnetoresistive head.
2. Description of the Related Art
Magnetoresistive elements are being adopted increasingly as the information reproducing element in magnetic tape and magnetic disk storage apparatus. The magnetoresistive element undergoes a resistivity change in response to a stray field from the recording medium, a phenomenon known as the magnetoresistance effect. The reproducing sensitivity of the magnetoresistive element is higher than that of the conventional inductive element, and is substantially independent of tape velocity and disk medium rotational speed. These characteristics make the magnetoresistive element quite effective in developing smaller magnetic tape drives, improving the recording density of magnetic tape media, enhancing the capacity of magnetic disk storage apparatus, and in making smaller-diameter magnetic disk media. Thus, magnetic heads equipped with the magnetoresistive elements are being used more and more.
FIG. 1 schematically illustrates a common configuration of a magnetic recording medium (magnetic tape or magnetic disk) and a magnetoresistive element in a magnetoresistive head. Between terminals 2, the magnetoresistive element 1 forms a single magnetic domain, and a bias field is applied to magnetize the magnetoresistive element 1 in a predetermined direction in the absence of a stray field from the recording medium. This region between the terminals 2 is the magnetic sensing part, where the magnetization direction tends to rotate from the normally-biased direction when the stray field 6 from the recording medium 4 is superposed on the bias field. The resistivity of the magnetoresistive element 1 changes in proportion to the rotation angle.
Thus, this region is effective in reproducing information, and the width of this region is the reproducing track width of the magnetic head. Shielding films 3 at both sides of the magnetoresistive element 1 prevent interference between stray fields 6 corresponding to plural information items, which stray fields distinguish each item of information even when the information is recorded at a high density on the recording medium 4.
The resistivity change in the magnetoresistive element 1 in response to the stray field 6 from the recording medium 4 can be converted into an electrical signal by detecting a voltage drop between the two terminals 2 when the sense current 5 supplied to the magnetoresistive element 1 is a constant current, or by detecting a change in the sense current 5 when a constant voltage is applied to the magnetoresistive element 1.
An example of a circuit configuration that may be used as a reproducing circuit for the magnetoresistive element 1 is shown in FIG. 2. In this configuration, the voltage applied to the terminals 2 is controlled by feedback through a low-pass filter 8 so that the sense current, the value of which is defined by an external resistor element 7, is supplied to the magnetoresistive element 1. Accordingly, the sense current 5 supplied to the magnetoresistive element 1 has a constant value that is not dependent upon the resistance of the magnetoresistive element 1. In this configuration, a change in the resistance of the magnetoresistive element 1 caused by the stray field 6 causes a change in the sense current 5 corresponding to the change of resistance, since a constant voltage is applied to the magnetoresistive element 1. This change in the sense current 5 is separated out as a reproduced signal by being converted to a voltage change through a load resistor 9.
A reproducing channel (of a magnetic disk storage apparatus, for example) which utilizes magnetoresistive elements as reproducing elements has generally a composition as shown in the block diagram of FIG. 3. The sense current defining resistor element 7 is connected to a read/write amplifier 10. The reproducing signal is obtained according to the principles described above, by supplying the sense current 5 defined by the resistor element 7 to the magnetoresistive element 1. The other illustrated portions of the reproducing channel are similar to those of the conventional reproducing channel that utilizes inductive elements.